Our previous work showed how global emissions of CFC-11 rose, starting in 2013, and that a substantial fraction of these emissions originated from eastern China. In two new papers, we show, using atmospheric observations, that these signals have now reversed. Montzka et al. (2021) uses measurements in the background atmosphere to show a rapid reduction in global emissions in 2019, and Park et al. (2021) identifies a coincident decline from China.
Dan Say’s work on our re-evaluation of the UK’s HFC emissions featured on the University of Bristol News. Based on an analysis of atmospheric data, we found that the UK’s estimates of the emissions of HFC-134a, used in car air conditioning, were likely too high. Dan took a closer look at the UK inventory and found that estimates of the frequency at which car air conditioning units were refilled, and the number of cars with air conditioning units in them were likely over-estimated in the inventory.
The government is now re-evaluating the assumptions that go in to their HFC-134a calculations.
In a new paper, published in the Proceedings of the National Academy of Sciences (PNAS), we examine the gap between the global emissions of HFCs that we infer from atmospheric observations and those reported by developed countries. The findings of the paper are summarised in a University of Bristol press release:
Until now, there has been little verification of the reported emissions of hydrofluorocarbons (HFCs), gases that are used in refrigerators and air conditioners, resulting in an unexplained gap between the amount reported, and the rise in concentrations seen in the atmosphere. This new study shows that this gap can be almost entirely explained by emissions from developing countries.
Currently only 42 countries are required to provide detailed annual reports of their emissions to the United Nations Framework Convention on Climate Change (UNFCCC).
The study, led by Mark Lunt from Bristol’s School of Chemistry used HFC measurements from the international Advanced Global Atmospheric Gases Experiment (AGAGE), in combination with models of gas transport in the atmosphere, to evaluate the total emissions that are reported to the UNFCCC each year.
HFCs are potent greenhouse gases; per tonne of emissions, each gas measured in this work is hundreds or even thousands of times more effective than carbon dioxide at trapping the radiation that warms the Earth.
There is currently no global agreement to regulate the emissions of these compounds, although proposals have been made to begin phasing out their use.
Mark Lunt said: “Any phase-out mechanism would likely be more stringent for the developed countries, but these results show that emissions from non-reporting countries are also highly significant.”
Meanwhile, the researchers note that although their estimates of total emissions from developed countries are broadly consistent with the reports that they compile, this does not necessarily mean that the emissions of each gas are being accurately reported.
In fact, the results suggest that the most commonly used HFC is significantly over-reported whilst some other HFCs are under-reported.
Dr Matt Rigby from the University of Bristol, who co-authored this work, said: “It appears as if the apparent accuracy of the aggregated HFC emissions from developed countries is largely due to a fortuitous cancellation of errors in the individual emissions reports.”
Professor Ron Prinn from the Massachusetts Institute of Technology (MIT), who leads the AGAGE network, added: “This study highlights the need to verify national reports of greenhouse gas emissions into the atmosphere. Given the level of scrutiny these reports are under at the moment, it is vitally important that we improve our ability to use air measurements to check that countries are actually emitting what they claim.”
I was recently interviewed for a report on the environmental impacts of refrigerant gases on behalf of a company that makes hydrocarbon refrigerant blends. The report is called “Hydrocarbons: The Quest For A Green Solution To The Changing Future Of Refrigeration And Air-Conditioning” is available on the PriorityCool Refrigerants website.
We recently published a paper “Recent and Future Trends in Synthetic Greenhouse Gases” in Geophysical Research Letters describing recent trends in “synthetic” greenhouse gases (gases with no significant natural sources), and their possible impact on climate in the coming decades. The paper was summarised on the American Geophysical Union blog (thanks to Alexandra Branscombe!), and is described in the following University of Bristol press release:
“The total warming impact of 25 major synthetic greenhouse gases has been examined by an international team, led by researchers from the University of Bristol.
The study estimates that, without additional limits on synthetic greenhouse gas use, the resulting increase in warming could outweigh the climate benefits gained thus far from phasing down chlorofluorocarbons (CFCs).
CFCs—commonly used in refrigerators and air conditioners—garnered public attention for their role in creating a hole in the ozone layer over Antarctica. As these chemicals were phased-down thanks to international agreements limiting their use, they were replaced by other synthesized gases that can still be harmful to the ozone layer and are greenhouse gases that contribute to climate change. Despite this, synthetic greenhouse gases (SGHGs) beyond the CFCs have received relatively little attention from the research community—until now.
The study, led by Dr Matthew Rigby in Bristol’s School of Chemistry, analysed observed atmospheric levels of SGHGs from 1978 to 2012, and then used these measurements to predict the impact these gases could have on global warming through 2050.
In response to the phase-down of CFCs through the 1987 Montreal Protocol, the researchers discovered that the use of other synthetic gases as refrigerants—such as hydrofluorocarbons (HFCs)—has risen. HFCs had been limited in the now-defunct 1997 Kyoto Protocol, but there is currently no agreement restricting their use. So, using HFCs as a test case, the researchers examined the effect of phasing down HFCs by amending the Montreal Protocol to include these gases.
Dr Rigby said: “We could avoid adding the equivalent of up to another three years of carbon dioxide emissions into the atmosphere if these gases were being phased down.”
HFCs are particularly strong greenhouse gases, so even relatively small levels in the atmosphere can contribute to warming.
“Per tonne of emissions, HFCs are much more potent greenhouse gases than carbon dioxide, and are very good at trapping the radiation that heats the Earth,” Dr Rigby said.
While HFCs are currently not a major driver of climate change compared to carbon dioxide or even other SGHGs, the researchers point out that if unabated they may contribute significantly to future warming.
The study used measurements of SGHG levels from the Advanced Global Atmospheric Gases Experiment (AGAGE), a global observing system developed by Professor Ronald Prinn of the Massachusetts Institute of Technology (MIT) and colleagues, and sponsored by NASA and other agencies.
Professor Prinn, co-director of the MIT Joint Program on the Science and Policy of Global Change and a co-author of the report said: “Addressing HFCs, and other SGHGs, now will ensure that they don’t contribute significantly to warming in the future.”
Meanwhile, the researchers note that due to extensive use, CFCs will continue to warm the planet for years to come.
“CFCs have contributed the most among the synthetic greenhouse gases to warming. Their use peaked and levels are now declining, but these gases will remain in the atmosphere for many years. This is likely the trend we will see with most SGHG gases, so it is important that we address these gases now before they do more severe damage,” said Professor Prinn.”
(With particular thanks to Audrey Resutek who wrote the MIT press release that this is based on).